The present invention is directed to a method for making thermoplastic polymeric products in the form of silicone-polyphenylene ether block copolymers and to thermoplastic blends of such block copolymers with polyphenylene ether. More particularly, the present invention relates to a method of oxidatively coupling monohydric phenol to polydiorganosiloxane having terminal monohydric phenol groups and to flame retardant products obtained therefrom.
Prior to the present invention, organopolysiloxane-polyphenylene ether block copolymers are shown by Kranz, U.S. Pat. No. 3,668,273, involving the reaction between hydroxy terminated polyphenylene ether segments and amine terminated polydiorganosiloxane segments. Another silicone-polyarylene ether block copolymer which can be made by effecting reaction between an amine terminated polydiorganosiloxane and anhydride functionalized-polyarylene ether is shown by Shea, et al, U.S. Pat. No. 4,814,392.
In copending application Ser. No. 07/455,122 filed Dec. 22, 1989, now abandoned, for Silicone Macromers and Thermoplastic Flame Retardant Silicone-Polyphenylene Ether Graft Copolymers Obtained Therefrom, phenol-siloxane macromers are shown. Some of these phenol-siloxane macromers are included within the formula, ##STR1## where R is selected from hydrogen, and the same or different radical selected from halogen, C(.sub.1-8) alkoxy, C(.sub.1-8) alkyl and C(.sub.6-13) aryl, R.sup.1 is a C(.sub.2-8) divalent aliphatic radical, R.sup.2 is selected from the same or different C(.sub.1-13) monovalent organic radicals, and n is an integer equal to 1 to 1000 inclusive. As taught in Ser. No. 07/455,122, now abandoned, if certain phenol-siloxane macromers having terminal phenol groups included within formula (1) where n is 10 to 30, are oxidatively coupled with a phenol, included within the formula, ##STR2## and there is used from 0.1 to 0.5 mol of macromer, per 100 moles of phenol, excessive cross-linking leading to gelation of the resulting block copolymer can be avoided.
It would be desirable therefore to be able to oxidatively couple phenol, such as a diorgano phenol to a siloxane macromer having terminal phenol groups over broad mol % ranges without having to be concerned with excessive cross-linking and gelation. The terms "gel" or "gelation" as used hereinafter means that the oxidative coupled reaction product is insoluble in organic solvents. Alternatively, the term "thermoplastic" means the ability to reversibly thermally mold or shape polymeric products at a temperature above their Tg and below their point of thermal decomposition produced by an oxidative coupling reaction in the form of silicone-polyphenylene ether block copolymer or a blend of such block copolymer and polyphenylene ether, referred to hereinafter as "composition".